> mine came off in a big way) and other assorted biofilms.  clean means 
> removing the cover and scrubbing the tank with a mild, non-abrasive 
> cleanser and pad combo.  i would reccomend the 3M dish washing pads 
> that have a pink sponge on one side and a *white* scrubby pad on the 
> other.  you do not want to scratch the plastic in cleaning as this 
> would give a nice home for bacteria to hide in.  get the tank clean 
> and white, period.
>From my work with biofilms, I can say the following:
clorox does work on biofilms so long as they are thin.  The clorox will
penetrate the biofilm and kill it.  Later, the biofilm will come off.  Thus,
just because you still have the goo stuck to the water tank after putting
clorox in, that does not mean that it is not dead.
However, I also have seen this:  If the biofilm is thick, and I mean 
something like an inch, the clorox can not penetrate the biofilm even after
several weeks.  Of course, if anyone lets biofilm 1 inch thick get in their
water tank, and then wants to drink the water, that is asking for trouble.
As it turns out, by the way, biofilm infections are among the most resistant
types of infections to control, being able to withstand about 500 times the
normal antibiotic dosage levels of other types of infections.